N. Undurraga, J.E. Araya, F. Zuazúa, and M.F. Alonso. 2020. Population dynamics of Melanaphis donacis (Hemiptera: Aphididae) and its Coccinellidae and Syrphidae predators on Arundo donax L. Int. J. Agric. Nat. Resour. 117-125. The population density of the aphid Melanaphis donacis (Passerini) was studied in experimental plots of Arundo donax (L.

RESUMENSe estudió la conducta de alimentación del depredador generalista Nabis punctipennis Blanchard (Nabidae) sobre Acyrthosiphon pisum Harris (Aphididae), dos hemípteros comunes en alfalfa en Chile, mediante un experimento en laboratorio utilizando A. pisum y Aphis craccivora Koch (Hemiptera: Aphididae) como presa alternativa, otro áfido común en alfalfa. La presencia de A. craccivora no afectó la depredación de A. pisum por N. punctipennis. La información obtenida sobre la conducta de depredación de N. punctipennis es valiosa para evaluar su potencial como agente de control biológico de A. pisum.Palabras clave: Nabis punctipennis, Acyrthosiphon pisum, Aphis craccivora, nábido de alas punteadas, presa alternativa, control biológico. ABSTRACTThe feeding behavior of the generalist predator Nabis punctipennis Blanchard (Nabidae) on Acyrthosiphon pisum Harris (Aphididae), two hemipterans common in alfalfa in Chile, was studied in a laboratory experiment using A. pisum, and Aphis craccivora Koch (Aphididae) as alternative prey, which is another common aphid in alfalfa. The presence of A. craccivora did not affect the predation of A. pisum by N. punctipennis. This finding on the predatory behavior of N. punctipennis is valuable to evaluate the potential of this nabid as a biological control agent of A. pisum.

Giant reed, Arundo donax (L.), is known for its potential as a bioenergy crop. To evaluate the effect of the aphid Melanaphis donacis (Passerini) on plants growing in the Metropolitan Region of Chile, three treatments with six plots each were compared: imidacloprid, the agricultural detergent TS2035, and an untreated control. Aphid density levels in the untreated control plants averaged 136.27 aphids leaf-1 along the growing season, while TS2035 and imidacloprid averaged 8.26 and 0.98 aphids leaf-1 , respectively. The greatest yield of A. donax (95.1 t dry matter (DM) ha-1) was obtained with the TS2035 detergent, followed by imidacloprid and the untreated control, with values of 88.8 and 84.1 t DM ha-1 , respectively. However, there were no significant differences (p ≤ 0.05) in DM yields of A. donax between treatments. Thus, control of M. donacis with insecticides would be unnecessary in bioenergy crops of A. donax in this region.